The present invention pertains to a hydraulic mount assembly, particularly adapted for automotive vehicle applications, having a control valve to provide bi-state soft and firm performance characteristics and including an annular decoupler which further improves high frequency vibration isolation capability of the mount in the low rate or soft operating mode.
Conventional vehicle powertrain mounts exist in many varieties and generally operate to provide engine vibration isolation while also controlling engine motion with respect to the vehicle frame or body structure. It has been recognized as desirable to provide a mount that exhibits relatively high damping responses or high dynamic stiffness for isolating or reacting low frequency relatively high amplitude vibrations and relatively low damping responses for isolating high frequency relatively low amplitude vibrations. For example, for vehicle power train control, it is desirable for the mount to provide higher damping and dynamic stiffness for low frequency, high amplitude inputs. At the same time, for the purpose of noise isolation, it is desired that the mount provide low dynamic stiffness at high frequency, low amplitude inputs.
One preferred type of mount which provides the above-recognized desiderata achieves its operating characteristics by allowing relatively free fluid pumping within the mount so that the mount deflects relatively easily thus minimizing the transmission of forces from the suspended or supported mass. Such a mount is also operable to provide relatively hard or stiff operating characteristics for controlling motion through transient, high amplitude vibrations or motion inputs. This operating characteristic is achieved by interrupting fluid flow from within the mount so that deflection of the mount causes an increase in pressure and contributes to an increase in mount stiffness.
U.S. Pat. No. 6,036,183 issued Mar. 14, 2000 to Chiung Alex Lee et al. pertains to a hydraulic mount which includes a valve positioned at a partition between the working chamber of the mount and the fluid reservoir. The valve body and the partition together define a control chamber in the fluid path and the control chamber is open to the reservoir through lateral openings in the valve body so that fluid pressure in the control chamber does not impose substantial biasing forces on the valve body or closure member and a small actuator can move the valve. When the valve is closed the fluid path is closed between the working chamber and the reservoir of the mount, thus providing for firm operational characteristics in controlling large amplitude inputs, such as those experienced from engine torque transients, for example. The subject matter of U.S. Pat. No. 6,036,183 is hereby incorporated herein by reference.
Additionally, however, it is desirable to provide a mount which provides for isolation of relatively low amplitude high frequency vibrations in the low rate or low stiffness operating mode. However, such a mount should also have cost, packaging, weight and performance advantages over a bi-state mount of the type described above as well as other bi-state mounts previously known. It is to these ends that the present invention has been developed.
The present invention provides an improved hydraulic mount, particularly adapted for vehicle powertrain mount applications, that provides both a high dynamic rate or dynamic stiffness and a low dynamic rate, and a decoupler to improve high frequency vibration isolation characteristics of the mount.
In accordance with one aspect of the present invention, a hydraulic mount is provided which comprises an upper elastomer housing or body, a base member and an orifice plate interposed the housing and the base member. The orifice plate is preferably integrally formed with a valve body for a generally cylindrical, so-called spool type valve closure member which is movable relative to the valve body to allow relatively free flow between fluid filled chambers in a first position. In a second position the valve closure member substantially restricts flow between the fluid filled chambers of the mount to control the mount operating characteristics. The orifice plate is provided with an annular decoupler member mounted thereon and retained in engagement therewith by a separable disc-like retainer member. Plural orifices in the orifice plate and the separable disc retainer member open to an annular recess containing the decoupler member to allow limited fluid flow through the orifices to provide for damping high frequency, low amplitude vibrations, in particular.
The hydraulic mount of the present invention overcomes the problems associated with prior art mounts with orifices which are tuned to provide a low dynamic rate at frequencies typically associated with engine idle (i.e., frequencies of about 25 to 50 Hz, depending on the engine). Hydraulic mounts with orifices that are tuned to provide a low dynamic rate at the aforementioned frequencies will have a high rate at frequencies only slightly higher due to the nature of fluid resonance. This characteristic can cause poor high frequency isolation characteristics of the mount.
Although decouplers are used in certain hydraulic mounts to overcome the aforementioned problem, packaging limitations in prior art mounts, including bi-state mounts in particular, have not provided for the incorporation of a decoupler in the mount. However, by providing an annular decoupler in the configuration according to the present invention, a mount is provided which is operable as a remotely controllable mount which also includes a decoupler to improve high frequency vibration isolation and provides a mechanically uncomplicated and compact design for improved cost and packaging considerations.
Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawing.